Aromatic hydrophobic polymers such as polysulfone and polyethersulfone are attractive as membrane polymers for one or more of the following reasons: a high glass transition temperatures, amorphous glassy state, thermal and oxidative stability, excellent strength and flexibility, resistance to extreme pHs, and low creep even at elevated temperatures. However, these polymers are inherently hydrophobic and therefore porous membranes made from these polymers are not wettable by water.
Attempts have been made to improve the surface wettability of porous membranes made from such polymers by numerous methods including coating and crosslinking a hydrophilic polymer, grafting of hydrophilic monomers by e-beam, gamma radiation, or UV or other radiation, surface oxidation, surface-initiated free radical grafting, blending with hydrophilic additives such as polyvinylpyrrolidone (PVP), copolymers of PVP, polyvinylalcohol (PVA), copolymers of PVA, polyethylene oxide (PEO), copolymers of PEO and polypropylene oxide, and in situ polymerization of hydrophilic monomers.
Drawbacks are associated with one or more of the above attempted methods. For example, with the methods involving blending of hydrophilic additives, the additives tend to leach out of the porous membrane on prolonged use in aqueous environments. Approaches involving coating and crosslinking a hydrophilic polymer tend to shrink or modify the membrane pores, thereby limiting the usefulness of the membranes.
The foregoing shows that there exists an unmet need for preparing porous membranes from aromatic hydrophobic polymers that would produce water wettable surfaces and the surface wettability would be stable over extended periods of use.